Inverters that supply a load such as a variable speed electric motor can not normally be paralled, a single unit unit of suitable size should normally be selected.
Some power inverters, but not all types, intended for off grid homes can be parralled, follow the manufacturers directions in such cases.
PV or wind turbine inverters that feed energy back into the grid are easily parraleled, after all how does the grid "know" the difference between two inverters in your home, and one in your home and one in your neighbours home, both on the same POCO transformer.